Peter West 
Sojourners [EPUB ebook] 

Katie and Jared are ordinary siblings who discover an extra-ordinary music box hidden in a local thrift store. They soon realize that it holds the key to a new reality, a dream world under siege by a necromancer and his legions of death. They are met there by noble unicorns, a clever squirrel, and an enigmatic stranger in possession of a familiar amulet bent on opening a long-forgotten portal. With the help of friends, new and old, they must rise above their years to fight a battle spanning the fabric of time and space in order to save a world beyond their own.